1. Field of the Invention
The present invention relates to a transmission apparatus, a reception apparatus and a digital radio communication method for digital radio communications.
2. Description of the Related Art
As a conventional digital modulation system, a technology described in Unexamined Japanese Patent Publication No. HEI 1-196924 is known. This is the technology whereby the transmitting side configures a frame by inserting one known pilot symbol per N data symbols and whereby the receiving side estimates a frequency offset and amount of amplitude distortion by using the pilot symbol and removes these frequency offset and amplitude distortion for demodulation.
Here, in the case of a radio communication, fluctuations in the transmission path occur due to fading and in terrestrial mobile communication in particular, fluctuations in the transmission path are not uniform. When fluctuations in the transmission path are intense, pilot symbols must be inserted at shorter intervals to prevent deterioration of the data demodulation error rate. On the contrary, when fluctuations in the transmission path are gentle, inserting pilot symbols at longer intervals does not severely deteriorate the data demodulation error rate.
On the other hand, when the level of a reception signal on the receiving side is small, a modulation system used must be highly resistant to errors for information symbol. On the contrary, when the level of a reception signal on the receiving side is large, higher priority can be given to a modulation system of high transmission efficiency for information symbol However, in the conventional digital modulation system above, the pilot symbol insertion interval and the information symbol modulation system are fixed. Therefore, when fluctuations in the transmission path are intense or the level of the reception signal of the receiver is small, error resiliency features during data demodulation reduces and the quality of data deteriorates. On the other hand, when fluctuations in the transmission path are gentle or the level of the reception signal on the receiving side is large, the data transmission efficiency cannot be improved regardless of data quality.